1. The Field of the Invention
This application relates generally to drilling methods and devices used in core drilling. In particular, this application relates to a method and apparatus for using polycrystalline diamond compact in reamers and other core drilling equipment.
2. Background and Related Art
Many drilling processes are currently known and used. One type of drilling process, exploration drilling, often includes retrieving a sample of a desired material from below the surface of the earth. In some processes used in exploration drilling, an open-faced drill bit is attached to the bottom or leading edge of a core barrel for retrieving the desired sample. The core barrel is then attached to a drill string, which is a series of connected drill rods that are assembled section by section as the core barrel moves deeper into the desired sub-surface formation. The core barrel is rotated, pushed, and/or vibrated into the formation to obtain a sample of the desired material (often called a core sample). Once the core sample is obtained, the core barrel containing the core sample is retrieved by removing (or tripping out) core barrel. The core sample can then be removed from the core barrel.
Reamers are sometimes used in the drill string to maintain a desired diameter of the borehole and to remove loose or uneven material from the walls of the borehole. Reamers are also sometimes used to maintain drill string alignment in the hole because the reamers have an outer diameter similar to the inner diameter of the hole, while the drill string is usually smaller than the diameter of the hole. Reamers are generally made using a steel tube that can be placed in line with the drill string. The steel tube may have abrasive pads or rings extending around the steel tube to achieve a desired stability for the drill string and/or to maintain the diameter of the borehole.
Maintaining consistent diameter from the top of the borehole to the bottom and clearance between the borehole walls and the drill string can facilitate removing and replacing of the drill string and allow space for drill cuttings clear. Accordingly, the reamer ensures the borehole does not press in on the drill string, which would require additional power to turn the drill string against the surface on significant portions of the borehole. A reamer may also minimize the surface area of the drill string in friction contact with the wall of the borehole while maintaining the lateral support for the drill string and reducing the energy required to turn and advance the drill string. In some applications, damaged or consumed reamers require tripping the entire drill string out for repairs or replacement with a new reamer.